1. Field of The Invention:
This invention relates to a steam generator for a fast breeder reactor having heat pipe structural walls which have high thermal conductivity being on the order of several times higher than the thermal conductivity of metals.
2. Description of The Prior Art:
In conventional steam generators, for example, tube and shell type steam generators, molten or liquid sodium is separated through a metal wall from water, such that the devices are structurally similar to a water loop steam generator.
Because an accidental break of the steam generator would result in a reaction of the radioactive liquid sodium with the water, an intermediate heat exchanger is provided in a primary cooling system so as to form a secondary sodium cooling loop for providing radio-inactive liquid sodium. The direct use of radioactive primary cooling liquid sodium in a steam generator has been considered and accordingly, a double walled tube, that is an outer tube covering an inner tube of the steam generator, has been proposed. However, the thermal conductivity of the wall is quite low so that this structure has not heretofore been employed. Accordingly, the secondary cooling loop is set in the primary cooling loop and the steam generator is set in the secondary cooling loop, so that should an accidental break occur, only the radio-inactive sodium is put into the steam generator, whereby the amount of damage from the accident is decreased.
However, as a present technology, it is difficult to make a steam generator in which there is no leakage of the liquid sodium. Moreover, it is presently necessary to provide a secondary cooling loop, and accordingly, the cost for construction of fast breeder reactors is remarkably higher than that of water reactors.
The conventional steam generator for a fast breeder reactor has the following disadvantages, because a steam generator for a water plant is presently used without modification:
1. It is necessary to use a secondary sodium cooling system;
2. When liquid sodium is used in the steam generator over a long period of time, a partition wall may accidentally be corroded by the molten sodium, whereupon because of the weakness thereof and subsequent failure of the wall, an accidental explosion may be caused by the reaction of the sodium with the water;
3. As a safety precaution, buildings and other constructions must have explosion resistant structure because of the consideration of such accidents, and the cost of construction accordingly is remarkably high;
4. While safety is relatively high when the partition wall of the steam generator is a double-tubed structure as hereinbefore indicated, the thermal efficiency, however, is low;
5. It is difficult to construct a reactor having no leakage from the partition wall, when an accident occurs in the steam generator; and
6. No detector for detecting a break of the partition wall of steam generators has heretofore been available. Even if such detection were available, the break occurs over a very short period of time, on the order of several seconds, and accordingly, since an increase in the amount of damage from the accident cannot be prevented within such a short period, plant operation overall is caused to be stopped.